Power driven tool



Jilly 23, 1940. T. L. HEDGPETH 2,208,843

POWER DRIVEN TOOL Filed May 7, 1938 3 Sfieets-Sheet 1 Ziaflezaior TermZ. jfeaj vei @wkeM/M July 23, 1940. T. 1.. HEDGPETH POWER DRIVEN TOOLFiled May 7, 1938 s Sheets-Sheet 2 W 0 H z A by m July 23, 1940.

\POWER DRIVEN TOOL Filed May '7, 195a T. L. HEDGPETH '4 3 Sheets-Sheet 3Patented July 23, 1940 r 2,208,843 POWER DRIVEN TOOL Theron L. Hedgpeth,Oak Park, Ill., assignor to Duro Metal Products Company, Chicago, 111.,a corporation of Illinois Application May 7, 1938, Serial No. 206,616

2 Claims.

This invention relates to power driven tools and particularly to powerdriven tools-such as scroll saws in which a flexible element, such asthe saw, is positively actuated at oneen-d and is subjected tocontinuous bias at the other end.

Such tools are driven at very high speeds, in fact, at speeds which arealmost vibratory in nature and the flexible members are subjected toundue strain and whip, particularly at the times l0 when the directionof movement is being reversed.

In accordance with the present invention I subject the flexible member,for example the saw blade, to spring tension at opposite ends sothat itis always maintained in a state of tension. I

applied at each end may be varied at will. Ordinary I find that the bestoperation is attained when the tension applied at opposite ends of theflexible member is approximately the same. I prefer to provide improvedspring means which are subjected to very little change in tension as aresult of the displacement to which they are subjected in the normaloperation of the tool. The invention will readily be understood from thefollowing description of a preferred embodiment thereof, taken inconjunction with the accompanying drawings, in which:

Fig. 5 is a fragmentary sectional view, taken on the line 5-5 of Fig..4, showing the pump I mechanism;

Fig. 6 is a fragmentary sectional plan view, taken on the line 6-6 ofFig. 3, showing the spring mechanism associated with the upper end ofthe scroll saw blade, and

Fig. '7 is a fragmentary sectional detail, taken on the line 1! of Fig.4.

Referring to the drawings, the improved saw comprises a base on which ismounted a motor I2 with the aid of an adjustable bracket M. The base I0carries a housing I6 within :which is provide simple means whereby thespring tension Figure 1 is a perspective view ofa scroll saw located thedrive mechanism I8 whereby the saw blade is reciprocated up and down. Onthe housing I6 is carried the air pump 26, which is best seen in Fig. 5.The lower spindle assembly 22 is mounted in the housing l6 and the worktable 24 is mounted on the housing l6 by means which will hereinafter bemore fully described.

The saw comprises an overhanging arm 26 which is secured to the base illby bolts 28. This arm is preferably hollow and comprises an uprightportion 36 and a horizontal overhanging portion 32 which extends aboveand over the work table 24. The horizontal portion 32 terminates in anenlarged hollow head 34. Within this head and within the adjacentportion of the horizontal portion 32 are located the upper spindleassembly 38 and the spring mechanism. 36. The upper spindle assembly 38is located in alignment with the lower spindle assembly The head 34 isnormally closed by a cover plate Ml, which is held in position by meansof screws 42. The hollow head 34 comprises upper and lower walls 44 and46 which carry bearings 48 in which the spindle 50 of the upper spindleassembly 38 reciprocates. The spindle 56 carries at its lower end achuck 52 which is adapted to receive the upper end of the saw blade 54which is secured thereto by means of the Wing nut 56.

The spindle 50 is cut away on opposite sides to provide fiat surfaces 58(Fig. 6) located at a portion of the spindle 50 which is always withinthe head 34. A pin 60 extends through the spindle 50 beyond the faces58. A bell crank lever 62 consisting of two similar members rivetedtogether and maintained in spaced relation, as indicated at 64, ispivotally mounted upon a pin 66 which extends across the horizontalhollow member 32 of the arm 26. The bell crank lever 62 includes a shortarm 68 which extends down-' wardly and a long arm Ill which extendshorizontally towards the spindle 50. The two spaced members of the bellcrank lever 62 are located on opposite sides of the spindle 5U engagingthe op- 50 against rotation. The extremities 12 of these members areslotted, as indicated at M, to receive the projecting ends of the pins60.

The short arm 68 is pivotally connected to a link 16 by a rivet pin 18.The opposite end of the link 16 is connected toone end of coil spring80, the other end of which is hooked to a threaded bolt 82 which extendspast the spindle 56 through an opening 84 in the cover plate 40. Theoutwardly projecting portion of the bolt '82 is provided with a. wingnut 86 so that the tension of I posite faces 58 thereof and holding thespindle I the spring may be adjusted at will. The bolt 82 is heldagainst rotation by suitable means, for example, its underside may beflattened as indicated at 88 (Fig. 6) and the opening 84 may be formedwith a corresponding flat side in engagement with the surface 88. Itwill be seen, with particular reference to Fig. 6, that the long arm 10of the bell crank lever 62 is offset, as indicated at 90, so as toenable the bolt 82 to be located to one side of the spindle 50.

A vertical rod 92 is adjustably mounted on the overhanging horizontalportion 32 of the arm 26, this rod being slidably and rotatably mountedin an opening in a boss 94 formed on one side of the arm 26. The rod 92is held in desired adjusted position by means of the thumb screw 96. Atits lower end the rod 92 carries a block 98 which is slidably mounted onthe rod 92, being positioned thereon in any desired location with theaid of a set screw I00. The block 98 is provided with an internal boreI02 which enters into a projecting nozzle I04 which is adapted to bedirected towards the work to blow the sawdust away.

Below the block 98, the rod 92 carries a supporting member I08, uponwhich is mounted a roller I96 provided with a V groove in which theblade 54 is received and guided. The supporting member I08 is adjustablymounted on a plate IIO by means of a knurled nut H2. The plate III] isprovided with a slot II4 through which extends a bolt II 6 whereby theplate is secured to the lower end of the rod 92 in desired position ofadjustment. The plate I I0 carries downwardly extending curved legs II8which are adapted to engage the work and prevent it from being elevatedby the return stroke of the blade 54.

The work table 24 is mounted upon a table support I22 which is securedto a bracket on the housing I6 by means of bolts I20. The table supportI 22 is provided with upwardly directed concave arcuate guides I24 andthe table 24 is provided with corresponding convex arcuate guides I26adapted to cooperate therewith. Consequently, the table can be tiltedabout the common axis of the arcuate guides I24 and I26, into anydesired inclination with respect to the saw blade.

The table may be locked in desired position of adjustment by handle andcam means designated generally by the reference numeral I28. The table24 is provided with an insert I29 which is located in substantialalignment with 'thespindle 50 and the lower spindle assembly 22, thisinsert being provided with a kerf through which passes the blade 54.This insert is removable to enable the machine to be used with toolsother than a ribbon saw blade, such as a file, saber saw, or sander, forexample. It may be noted that when thus employed, the overhanging arm 26may readily be romoved by removing the bolts 28, thereby providingunlimited work room above the table. When thus used, the tool is rigidlymounted in the lower spindle assembly 22.

Referring more particularly to Figs. 3 and 4, it will be noted that thehousing I6 provides a cylindrical crank case chamber I30 which isprovided with a vertical boss I32 on its upper side. Bearing members I34are located within the boss for slidably supporting the lower spindleI36 of the lower spindle asembly I22. The upper end of the spindle I36is provided with a chuck similar to that carried by the upper spindle50.

The spindle I36 is provided on one side with a horizontal rectangularslot. I 38. Opposite this slot it is provided with a flat surface I40. Ahorizontal guide block I46 is rigidly seated within the slot I38 and isheld therein by means of a bolt I42 which extends through the block I46and is threadedly received in a bore I44 which extends through thespindle I36 from the slot I38 to the flat face I40. The bolt I42 issecurely locked in position by means of an internally threaded sleeveI86 which is provided with a hexagonal portion I88 near its inner endand a cylindrical portion I projecting outwardly therefrom.

The guide block I46 is provided with a longitudinal bore I48 ofcylindrical section, which bore is open to the outer side of the blockI46, that is, to the left side as viewed in Fig. 4. A cylindrical blockI50 is located within the block I46 so as to reciprocate freely thereinin a horizontal direction. A crank pin I54 extends freely into ahorizontal bore I52 in the block I50. The manner in which the crank pinI54 is actuated will be hereinafter described. It will, however, benoted that when this crank pin is rotated it effects the reciprocationof the spindle I 36 in the upward and downward direction. At the sametime Una block I54 reciprocates horizontally in the bore I48 in theblock I46. It is to be noted that the block I50, being held againstmovement about the axis of the spindle I36 by engagement with the crankpin I54, effectively prevents rotation of the spindle I36.

The left-hand side of the housing I6, as viewed in Fig. 4, is closed bymeans of a cover I58, a gasket I60 being interposed between the flangeof the cover and the adjacent flange of the housing. The cover I58 has atransverse bore I62 through which extends a drive shaft I64, the shaftbeing supported by suitable bearings I66. The cover I58 comprises acylinder I68 at right angles to the bore I62. I

A piston stem I'I0 extends downwardly through an opening in the lowerend of the cylinder I68 and contacts a cam I'I2 formed on the driveshaft I64 so as to effect reciprocation of the piston stem. The piston,which is provided with a suitable sealing cup at its upper end, isbiased downwardly by a spring H4. The cylinder I68 is provided with airpassages I76. The outlet of the pump is connected by a flexible hose I18to a nipple on the block 98 which connects to the internal bore I02 and,consequently, to the projecting nozzle I04. The flexible conduit Il8 maypreferably extend into the base I0 and through the overhanging arm 26 toa position adjacent the block 98.

The crank pin I54 is rigidly mounted in a balanced crank I 80 which, asbest seen in-Figs. 3 and 4, consists mainly of ,a counterweight portionlocated on the side of the shaft I64 which is opposite the position ofthe pin I54. The crank member I80 is rigidly mounted on the inner end ofthe shaft I64. The outer end of the shaft I 64 carries a variable speedpulley I82 which is driven by means of a V belt I84 from a correspondingvariable speed pulley (not shown) on the motor I2. v

The cylindrical portion I90 of the sleeve I86 serves as an abutment forthe hook-curved end I92 of a fiat spirally wound spring I94. The innerend of the spring I94 is mounted in a transverse slot I 96 of a shaftI98 upon which it is held by means of nuts 200. The shaft I98 isrotatably mounted in a boss carried by the cover 292 which closes theend of the housing 204 opposite the cover I58. The shaft I98 is providedat its outer end with a hexagonal head 206 which is received in ahexagonal opening 2 I4 in a handle 208.

The handle 268, which is slidably mounted on the shaft I98, is recesedto accommodate a spring 2 Nil This spring, which is accommodated aroundthe shaft iSB, abuts against the inner side of the head 2% and againstthe shoulder N2 of the handle 2E8 so as to force the handle inwardlytowards the cover 282. The innermost end 213 of the handle 2%, whichnormally bears against the cover 262, is provided with a circumferentialseries of openings 226, as best seen in Figs. 4 and '7. The cover 202has rigidly mounted therein an outwardly projecting pin 22 which isadapted to enter any of the openings 22!? which may be presented to it.It will be readily understood that if the handle 288 is pulled outwardlyit may be rotated in either direction so as to adjust the tension whichthe spring 194' applies to the sleeve I86. When the tension is thusregulated, the handle 208 is allowed to move inwardly under the actionof the spring 2 l6 and the pin 222 enters the adjacent opening 220 sothat the tension of the spring is maintained in the desired condition.

The weighted crank N38 is arranged to provide a substantial balance forthe moving systemcomprising the spindle 136, the blade 54 and thespindle 50. This balance is necessarily somewhat approximate, becausethe load experienced by this system in moving downwardly varies widely,depending upon whether or not the blade 54 is cutting.

In the ordinary operation of tool of this kind, the spindle 22 is pulleddown forcibly by the crank pin I54 and when the crank pin i5 1 passesthrough its lowest position. the downward load on the spindle isreleased and the spindle is free to move relative to the crank pin I54Within the limits of the lost motion necessary between these elementsfor working fit. This relative freedom and the initiation of the returnmovement of the tool, due to the tension of the spring 8!! and also tothe drive by the crank pin, result in whipping and irregular movementsof the blade Be.

In my present structure such defects are completely avoided because theblade 54 is maintained under tension at all times. Further, the springs80 and H94 counter-balance each other to a considerable extent and themajor operating force is that applied by the crank pin I54 which is, infact, responsible for practically all movements, both up and down, ofthe blade 54.

In practice, I prefer that the upward force exerted on the blade by thespring 80 should be approximately equal to the downward force applied tothe blade by the spring 19%. However, it is not necessary to measurethese forces since the machine is adapted for very perfect adjustment inthe following manner. The wing nut 86 is tightened in order to apply areasonable degree of tension to the spring 8t. If no tension is appliedto the spring Hi l and the motor I2 is started, the machine will workwith a pronounced noise due to whipping and irregular movements of theblade and also due to lost motion between the pin W4 and the spindleI36. If, now, the spring I95 is tensioned by suitable displacement ofthe handle 258, the noise will lessen and lessen progressively and canbe substantially eliminated. If too much tension is applied to thespring I9 5, the operation again becomes noisy and this occurrenceindicates that the handle 26% should be backed up again to reduce thetension of the spring 18 to a degree which is approximately equal tothat exerted on the spindle 5G by the spring Bil.

It is to be noted that both these springs adapted to apply a veryuniform tension upon the'two spindles with which they are associated.That is, the tension of a spring like the spring 85 increases withextension. This effect can'be minimized by using a very long spring. Iam able to use quite a short spring 85 while obtaining very uniformtension on the spindle 5i) by my new feature of employinga bell cranklever Bil of very considerable leverage. The coil type of spring Hi4provides the eifect of a relatively long spring while occupying arelatively small space.

Although the invention has been disclosed in connection with thespecific details of a preferred einbcdimezzit thereof, it must beunderstood that such details are not intended to be iimitative of" theinvention except insofar as set forth in the accompanying claims.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent of the United States is:

1. In a scroll saw, the combination comprising, a base, an overhangingarm mounted on the base having a substantially horizontal hollow portionat its overhanging end and a cover closing said hollow portion, a memberextending vertically through the hollow portion .near said end andmounted to reciprocate therein, a bell crank within the hollow portionpivotally mounted rearwardly of said member, said bell crank having along substantially horizontal arm extending forwardly of the pivotalmounting and a relatively short substantially vertical arm, a linkpivotally attached to the outward end of said vertical arm, means toconnect said long arm to said member, a horizontally positioned springsecured to said link, and manually operable means outside of said hollowportion to adjust the bias of said spring, the last said meanscomprising a threaded member secured at one end to said spring andprojecting through an opening in said-cover, and the portion of saidthreaded member projecting through said cover having a complementarythreaded manually adjustable member threaded thereto.

2. In a scroll saw blade reciprocating unit, in

combination, a housing and a cover to close said housing, a reciprocablemember extending into the housing, a spiral spring having a hooked outerend engaging said reciprocable member to bias said member downwardly, acontrol shaft extending into said housing and engaging the inward end ofsaid spring, control means outside of said housing adapted by manualmanipulation to rotate said controlshaft, and means to secure saidcontrol shaft in any manually set position, said control shaft journaledthrough said cover and extending beyond the outer face thereof, saidcontrol means secured to the outer end of said control shaft and saidcover carrying the means to secure the control shaft in any manually setposition, whereby the control shaft, the spiral spring, the controlmeans, and

the means'to secure the control shaft are all removable from the sawblade reciprocating unit as a single unit with said cover.

'IHERON L. HEDGPEfII-I.

